What is the difference between the antiprotozoal drugs ornidazole, levornidazole and levornidazole disodium phosphate❓❓❓

Ornidazole is a third-generation nitroimidazole. It has an antagonistic effect on protozoa such as amoeba, trichomoniasis, and giardiasis. In addition, it also has a good anti-anaerobic effect. So, what is the difference between ornidazole, levornidazole and levornidazole disodium phosphate?

Antiprotozoal effect and anti-anaerobic bacteria effect.

For the treatment of anaerobic and protozoal infections, metronidazole, tinidazole, ornidazole, and levornidazole can be used. Secnidazole can only be used for the treatment of protozoal infections. Tinidazole and ornidazole are more resistant to anaerobic bacteria than metronidazole. These drugs have smaller molecular weight, better lipid solubility and poor water solubility. They can enter the placenta and cerebrospinal fluid.

Indications and dosage.

Ornidazole is a racemic compound. It is converted in the body to dexornidazole and levornidazole. Both of them have similar antiprotozoal and antianaerobic abilities. However, dexornidazole is more toxic than levornidazole. The half-lives of ornidazole and levornidazole are 12 to 14 hours and they have the same indications and dosages. The indications and dosage of ornidazole and levornidazole are as follows:

To treat anaerobic infections: 

• After dinner, take 1.5g orally, and take the medicine continuously for 1 to 3 days according to the condition.
• Take 0.5 to 1 g orally each time, once every 12 hours, and take the medicine continuously for 3 to 10 days according to the condition.
• The starting dose by intravenous infusion is 0.5 to 1 g every 12 hours for 5 to 10 days.

To treat trichomoniasis:

• After dinner, take 1.5g orally, and take the medicine continuously for 1 to 2 days according to the condition.

For the treatment of vaginal trichomoniasis, it is recommended that a single dose of metronidazole 2g or a single dose of tinidazole 2g is recommended.

Adverse reactions.

Common adverse reactions of nitroimidazoles are as follows:

• Oral gastrointestinal adverse reactions such as metallic taste, stomach pain, and nausea.
• Nervous system side effects such as numbness, spasms, tremors, dizziness, headache, and confusion in the limbs.

The incidence of gastrointestinal adverse reactions was similar between ornidazole and levornidazole. Taking ornidazole and levornidazole after meals can reduce gastrointestinal adverse effects. However, ornidazole has a higher incidence of neurological adverse effects than levornidazole. 

Nitroimidazoles can cause disulfiram-like reactions. They inhibit acetaldehyde dehydrogenase and prevent hepatic oxidative metabolism of acetaldehyde. It causes acetaldehyde to build up. Nitroimidazoles may also inhibit dopamine beta-hydroxylase activity and reduce dopamine metabolism. It increases dopamine levels in the brain leading to serotonin toxicity syndrome. Compared with other nitroimidazoles, ornidazole has less inhibitory effect on acetaldehyde dehydrogenase. However, it has also been reported that ornidazole can cause a disulfiram-like reaction. Therefore, it recommends that alcoholic beverages or medications should not be taken while taking ornidazole.

Difference between levornidazole and levornidazole phosphate disodium.

Levornidazole has poor water solubility. In order to enhance its water solubility, it is generally added with hydrochloric acid. This lowers the pH of the injection to 3.2 to 4.5. Injections with low pH are more likely to cause phlebitis.

The water solubility of levornidazole disodium phosphate will be higher than that of levornidazole. Its injectable dosage form has a pH of about 5.5. Some studies have pointed out that levornidazole phosphate disodium injection does not cause phlebitis.

When ornidazole and levornidazole are administered intravenously to patients, the injection should be diluted to a solution of ≤5 mg/ml. In addition, each intravenous infusion of 100ml of solution, the infusion time is not less than 30 minutes. Ornidazole and levornidazole injections should be stored in a shaded, airtight and cool place (temperature not exceeding 20°C).